DRBD was nice to use. Great thing about it is that you can put it below the existing filesystem. I don't remember how it works, maybe it puts metadata at the en

DRBD was nice to use. Great thing about it is that you can put it below the existing filesystem. I don't remember how it works, maybe it puts metadata at the end of block device so filesystem should be shrinked before I remember moving a huge NFS partition which was experiencing constant writes to another server with DRBD. With almost zero downtime. So is a nice tool if you want to move a filesystem with such huge amount of files that even iterating over the file tree takes hours